Moon and planets will put on a show

Jupiter, Venus will appear to touch

On Monday evening, the three brightest objects in the night sky will dance.

Jupiter and Venus, which for weeks have been edging closer to each other in the southwestern sky, will appear to nearly touch -- and on Monday after sunset, the crescent moon will join them.

"They're going to be so close that if you held your thumb at arm's length, you'd actually be able to cover all three objects with your thumb," said Richard McColman, star theater director at Morehead Planetarium and Science Center in Chapel Hill.

In centuries past, people saw the alignment of planets as omens of war, plagues, the rise of kings. A previous conjunction (that's the term astronomers use) of Jupiter and Venus about 2 B.C. is one explanation offered by astronomers for the star of Bethlehem.

"That conjunction was so close, according to computer calculations, that to the naked eye, the two planets would have appeared to merge in the sky into one very bright object," McColman said.

Of course, the three celestial bodies are not actually close to each other; they're simply positioned so that they appear close together when viewed from Earth.

In modern times, planetary conjunctions have lost their mystical import, but they still have a celestial allure.

"Conjunctions are common," said Mike Castelaz, science director at Pisgah Astronomical Research Institute, a nonprofit foundation in Rosman. "The difference is how close the planets get to each other. The planets will be about 2 degrees apart."

"This one is fairly rare," he said; Jupiter and Venus will not appear so close together again until March 2012.

Even rarer is when the planets actually appear to touch. Venus and Jupiter last crossed paths in 1818 and won't again until 2065, Castelaz said.

To see the alignment, look in the southwestern sky shortly after dark on Monday. If the weather is clear, you won't miss them: The three objects will be closely bunched about a fifth of the way up from the horizon at 5:30 p.m. By 7:30, they will slip down on the horizon.

The term "bunched" is relative. The moon is about 238,000 miles from the Earth.

The distance between Earth and the planets varies according to their position in orbit around the sun. Jupiter is now about 535 million miles from Earth. It's by far the largest planet in the solar system -- twice the size of all the other planets combined.

Venus, now about 93 million miles from Earth, is slightly smaller than Earth but so much closer than Jupiter that it appears brighter.